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Marco Realacci 2025-03-25 09:13:01 +01:00
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3
.obsidian/workspace.json vendored
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@ -231,9 +231,9 @@
}, },
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"Pasted image 20250325090735.png",
"Concurrent Systems/slides/class 8.pdf", "Concurrent Systems/slides/class 8.pdf",
"Concurrent Systems/notes/8 - Enhancing Liveness Properties.md", "Concurrent Systems/notes/8 - Enhancing Liveness Properties.md",
"Pasted image 20250325090735.png",
"Concurrent Systems/notes/7- MUTEX-free concurrency.md", "Concurrent Systems/notes/7- MUTEX-free concurrency.md",
"Concurrent Systems/notes/images/Pasted image 20250324091452.png", "Concurrent Systems/notes/images/Pasted image 20250324091452.png",
"Concurrent Systems/slides/class 7.pdf", "Concurrent Systems/slides/class 7.pdf",
@ -264,7 +264,6 @@
"Pasted image 20250318090909.png", "Pasted image 20250318090909.png",
"Pasted image 20250318090733.png", "Pasted image 20250318090733.png",
"Concurrent Systems/slides/class 5.pdf", "Concurrent Systems/slides/class 5.pdf",
"Concurrent Systems/notes/images/Pasted image 20250317105355.png",
"HCIW/slides/4 HUI2016-6-forcefeedback.pdf", "HCIW/slides/4 HUI2016-6-forcefeedback.pdf",
"HCIW/slides/3b Haptic slides.pdf", "HCIW/slides/3b Haptic slides.pdf",
"HCIW/notes/2 - Interface and Interaction for IoT.md", "HCIW/notes/2 - Interface and Interaction for IoT.md",

20
Concurrent Systems/notes/8 - Enhancing Liveness Properties.md
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@ -16,6 +16,8 @@ Can we take the most basic protocol that satisfies the most basic liveness prope
REMARK: the moment in which all variables contain the same leader is unknown REMARK: the moment in which all variables contain the same leader is unknown
#### From obstruction-freedom to non-blocking
``` ```
NEED_HELP[1..n] : SWMR atomic R/W boolean registers init at false NEED_HELP[1..n] : SWMR atomic R/W boolean registers init at false
@ -57,4 +59,20 @@ It can be proved that there exists no wait-free implementation of $\Omega$ in an
REMARK: $\tau_{1}, \tau_{2}, \nabla$ and $p_L$ are all unknown. REMARK: $\tau_{1}, \tau_{2}, \nabla$ and $p_L$ are all unknown.
![[Pasted image 20250325090735.png]] IDEA:
- `PROGRESS[1..n]` is an array of SWMR atomic registers used by proc’s to signal that they’re alive
- pi suspects pj if pi doesn’t see any progress of pj after a proper time interval (to be guessed) set in its timer
- the leader is the least suspected process, or the one with smallest/biggest ID among the least suspected ones (if there are more than one)
- this changes in time, but not forever
Guessing the time duration for suspecting a process:
- SUSPECT[i,j] = #times pi has suspected pj
- For all k, take the t+1 minimum values in SUSPECT[1..n , k]
- Sum them, to obtain Sk
- The interval to use in the timers is the minimum Sk
- it can be proved that this eventually becomes ≥ $\nabla$
#### From obstruction-freedom to wait-freedom
**Eventually perfect:** failure detector ♢P provides each process $p_i$ a local variable $suspected_i$ such that
1. *(Eventual completeness)* eventually, $suspended_{i}$ contains all the indexes of crashed processes, for all correct $p_i$
2. (*Eventual accuracy*)